HP-41 Card Reader

The HP-41 allows for programming the keys to be assigned as you wished, an
interesting capability which was normally quite constructive, but with a
little thought .....

Our department had just been issued new HP-41s with options as requested
by the engineers. Many of us had the card readers and additional ROM modules.
The next day one of the mechanical engineers had proudly announced that he
had been able to throw away his "Little Black Book", as he had programmed
all the names and addresses into his new calculator. A day or two later,
I went in and asked his advice on a program problem I had. I asked if I could
run the program on his machine as I thought that my card reader had a problem.
He insured me that I had a program bug, and took the program card and loaded
it into his calculator. When the load was finished he hit a key and the
calculator turned off, so I told him that that was the same as what had happened
to me. An hour or so later he came into my office after he figured out that
what I had done was to program every possible keystroke as an "Off" button.
He finally had to do a hard reset, and lost all the names and addresses of
his girlfriends.